LIBS applicability for investigation of re-deposition and fuel retention in tungsten coatings exposed to pure and nitrogen-mixed deuterium plasmas of Magnum-PSI

We have investigated the applicability of Laser Induced Breakdown Spectroscopy (LIBS) for analyzing the changes in the composition and fuel retention of W and W-Ta coatings following exposure to D2 or mixed D2-N2 plasma beams in the linear plasma device Magnum PSI. The exposed samples were characterized by in situ ns-LIBS and complementary analysis methods Secondary Ion Mass Spectroscopy, Energy Dispersive x-ray spectroscopy and Nuclear Reaction Analysis. In agreement with the used complementary analysis methods, LIBS revealed the formation of up to 400 nm thick co-deposited surface layer in the central region of the coatings which contained a higher concentration of the main plasma impurities, such as N, and metals, such as Ta and Mo, the latter originating mainly from the substrate and from the plasma source. The deuterium retention on the other hand was highest outside from the central region of the coatings.</p

ОПТИМИЗАЦИЯ РАЗМЕЩЕНИЯ ОБЪЕКТОВ С УЧЕТОМ ИХ РЕПЛИКАЦИЙ НА УЗЛАХ РАСПРЕДЕЛЕННОЙ ИНФОРМАЦИОННО-ВЫЧИСЛИТЕЛЬНОЙ СИСТЕМЫ

Предлагается модель размещения объектов на узлах распределенной системы, учитывающаявведение репликаций, параметры объектов и потоков запросов к объектам, характеристики каналов передачи данных и узлов обработки запросов. Формулируется оптимизационная задача распределения объектов на узлах, предлагается алгоритм наискорейшего спуска решения задачи. Проводятся эксперименты, выявляющие закономерности и тренды в изменении параметров функционирования оптимизированной системы

Plasma-wall interaction studies within the EUROfusion consortium: Progress on plasma-facing components development and qualification

This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.The provision of a particle and power exhaust solution which is compatible with first-wall components and edge-plasma conditions is a key area of present-day fusion research and mandatory for a successful operation of ITER and DEMO. The work package plasma-facing components (WP PFC) within the European fusion programme complements with laboratory experiments, i.e. in linear plasma devices, electron and ion beam loading facilities, the studies performed in toroidally confined magnetic devices, such as JET, ASDEX Upgrade, WEST etc. The connection of both groups is done via common physics and engineering studies, including the qualification and specification of plasma-facing components, and by modelling codes that simulate edge-plasma conditions and the plasma-material interaction as well as the study of fundamental processes. WP PFC addresses these critical points in order to ensure reliable and efficient use of conventional, solid PFCs in ITER (Be and W) and DEMO (W and steel) with respect to heat-load capabilities (transient and steady-state heat and particle loads), lifetime estimates (erosion, material mixing and surface morphology), and safety aspects (fuel retention, fuel removal, material migration and dust formation) particularly for quasi-steady-state conditions. Alternative scenarios and concepts (liquid Sn or Li as PFCs) for DEMO are developed and tested in the event that the conventional solution turns out to not be functional. Here, we present an overview of the activities with an emphasis on a few key results: (i) the observed synergistic effects in particle and heat loading of ITER-grade W with the available set of exposition devices on material properties such as roughness, ductility and microstructure; (ii) the progress in understanding of fuel retention, diffusion and outgassing in different W-based materials, including the impact of damage and impurities like N; and (iii), the preferential sputtering of Fe in EUROFER steel providing an in situ W surface and a potential first-wall solution for DEMO.European Commission; Consortium for Ocean Leadership 633053; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Determination of Heating Value of Estonian Oil Shale by Laser-Induced Breakdown Spectroscopy

The laser-induced breakdown spectroscopy (LIBS) combined with multivariate regression analysis of measured data were utilised for determination of the heating value and the chemical composition of pellets made from Estonian oil shale samples with different heating values. The study is the first where the oil shale heating value is determined on the basis of LIBS spectra. The method for selecting the optimal number of spectral lines for ordinary multivariate least squares regression model is presented. The correlation coefficient between the heating value predicted by the regression model, and that measured by calorimetric bomb, was R2=0.98. The standard deviation of prediction was 0.24 MJ/kg. Concentrations of oil shale components predicted by the regression model were compared with those measured by ordinary methods

Development of laser-induced breakdown spectroscopy for analyzing deposited layers in ITER

Laser-induced breakdown spectroscopy (LIBS) experiments on different ITER-relevant beryllium-tungsten mixtures were performed to develop LIBS for tokamak applications. Some of the samples were doped or implanted with deuterium to simulate fuel retention. The results indicate that beryllium and tungsten have a number of distinguishable spectral lines for diagnostics purposes, but detection of deuterium is challenged by its low concentration and low fluences used. By studying the depth profiles of the coatings, the removal rates of the layers were observed to depend on the thickness, composition and deuterium content of the coating. Quantitative studies of the compositions were made by calibration-free LIBS, and the results agreed well with those given by ion-beam methods

In-situ LIBS and NRA deuterium retention study in porous W-O and compact W coatings loaded by Magnum-PSI

The purpose of this study is to investigate the applicability of in-situ laser induced breakdown spectroscopy (LIBS) for deuterium retention measurements in tungsten coatings with different morphology and oxygen content. These were exposed to a Gaussian beam of deuterium plasma in the Magnum-PSI linear plasma device. The deuterium line intensities determined by LIBS were compared with the deuterium content measured by nuclear reaction analysis (NRA). Both LIBS and NRA results showed that higher deuterium retention was achieved in the coating region corresponding to the periphery of the plasma beam. This decreasing deuterium retention in the central region can be attributed to higher surface temperature. At the same time, the deuterium retention in different coating types assessed by LIBS D intensity was markedly different from the retention determined by NRA. Porous W-O coating with high oxygen content had the highest deuterium retention according to NRA while D intensity obtained by LIBS was an order of magnitude smaller when compared with other coatings. The deuterium retention in compact W coating and thick W coating was almost the same and LIBS D intensities were also comparable for these coatings. The results demonstrate the LIBS applicability and its limits in different coating types.</p

In-situ LIBS and NRA deuterium retention study in porous W-O and compact W coatings loaded by Magnum-PSI

The purpose of this study is to investigate the applicability of in-situ laser induced breakdown spectroscopy (LIBS) for deuterium retention measurements in tungsten coatings with different morphology and oxygen content. These were exposed to a Gaussian beam of deuterium plasma in the Magnum-PSI linear plasma device. The deuterium line intensities determined by LIBS were compared with the deuterium content measured by nuclear reaction analysis (NRA). Both LIBS and NRA results showed that higher deuterium retention was achieved in the coating region corresponding to the periphery of the plasma beam. This decreasing deuterium retention in the central region can be attributed to higher surface temperature. At the same time, the deuterium retention in different coating types assessed by LIBS D intensity was markedly different from the retention determined by NRA. Porous W-O coating with high oxygen content had the highest deuterium retention according to NRA while D intensity obtained by LIBS was an order of magnitude smaller when compared with other coatings. The deuterium retention in compact W coating and thick W coating was almost the same and LIBS D intensities were also comparable for these coatings. The results demonstrate the LIBS applicability and its limits in different coating types